Oh sorry, I thought you meant four different programming languages, lol dunno what I was thinking.
But I think I would still do it the same way with building the four separate sites with different languages and having each language in separarte directories. Then you could even auto detect the visitors browsers default language and redirect them to the appropriate file.
What you're wanting to do with four separate languages and one set of files I think would require you to make a language file with variables for each word you're going to be using on your website.
lang[web design]=Web Design
lang[web design]=El Diseรฑo de la telaraรฑa
That's just an example, but you'd need one for each word in each language. It may be best to make these in four separate files, one for each language.
Then you would have to set cookies or something like that when they select their language so it can remember which words to use. So you'd have to have something like if language = french then include your french language file else if language = spanish then include your spanish language file and in your code each word would need to be printed as a variable such as lang[web design] which would print the correct word based on the file you included.